This invention relates to a variable speed hydraulic turbine generator apparatus utilizing an induction generator and a secondary excitation controller connected to the secondary side of the induction generator and more particularly to a control system for variable speed hydraulic turbine generator apparatus which is suitable for realizing running and frequency control at a maximum efficiency point.
One of major objectives of performing speed control for a rotary electric machine is to realize a running of the rotary electric machine at a maximum efficiency point of a turbo-machine by controlling the rotation speed of the rotary electric machine in accordance with a load, such as a pump hydraulic turbine, on the turbo-machine. There are available two major methods for variable speed operation of a hydraulic turbine of a hydraulic turbine generator apparatus.
The first one is the provision of a frequency converter between an AC power line system and a generator. JP-A-48-21045 proposes a method wherein supply of power to the AC power line system can be ensured even when the generator is operated at any desired speeds and the rotation speed is adjusted by regulating a guide value of the hydraulic turbine to realize a running at a maximum efficiency point of the hydraulic turbine.
The second method is to connect the primary side of a wound-rotor type induction machine to the AC power line system and to provide a frequency converter between the secondary side and the AC power line system. This method has hitherto been known as a typical way of controlling the rotation speed in accordance with the output of the generator and is described in, for example, the Electrical Engineering Handbook published by the Institute of Electrical Engineers of Japan in 1967. Control systems for this type of variable speed hydraulic turbine generator apparatus have been proposed as disclosed in, for example, JP-A-52-46428, specification and drawings of Japanese patent application No. 57-182920, and JP-A-55-56499.
A common task shared by the above two types of variable speed hydraulic turbine generator apparatus resides in how the hydraulic turbine output and the generator output are controlled to control the rotation speed. More specifically, the task is directed to how to use, for controlling the outputs of the hydraulic turbine and the generator, a speed different signal (Na-N) resulting from a comparison between an optimum rotation speed command Na calculated from a signal containing an external generator output command signal Po supplied externally to indicate a hydraulic turbine running condition and a rotation speed detection value N. This is because, in an arrangement comprises of a hydraulic turbine and a generator mechanically coupled thereto, it is general that kinetic energy of a fluid flow in the water channel is on the one hand less than kinetic energy of rotation of the mechanical system, i.e., the hydraulic turbine and that loss of the generator is, on the other hand, almost negligible in regulation of the rotation speed, with the result that the difference between the outputs of the hydraulic turbine and generator almost corresponds to an increase or decrease in the kinetic energy of rotation and hence may be used for regulation of the rotation speed of the generator. The external generator output command Po herein referred to means a generator output command other than an internal output command which may be calculated from measured signals representative of voltage, current, frequency, phase and rotation speed of components such as the hydraulic turbine, generator and frequency converter which constitute the variable speed generator apparatus. Specifically, the external generator output command is externally supplied from a central power feed commanding station.
In the aforementioned JP-A-55-56499 proposing a control system for variable speed hydraulic turbine generator apparatus wherein the wound-rotor type induction machine is connected at its secondary side to the AC power line system and the frequency converter is provided between the secondary side and the AC power line system, three kinds of measured signals representative of the speed of drive medium (water flow rate in the case of hydraulic turbine), rotation speed and output of generator stator are employed for controlling the outputs of the generator and hydraulic turbine. This publication however fails to suggest a specified manner of controlling the outputs of the generator and hydraulic turbine. It also fails to suggest how the generator output should respond to the external generator output command Po.
The aforementioned JP-A-52-46428 and specification and drawings of Japanese patent application No. 57-182920 proposing another control system for variable speed hydraulic turbine generator apparatus suggest a control method wherein a rotation speed difference signal is used for controlling the generator output.